RNA interference initially discovered in plants as Post-Transcriptional Gene Silencing (PTGS), is a highly conserved mechanism triggered by double-stranded RNA (dsRNA) and able to down regulate transcript of genes homologous to the dsRNA1. The dsRNA is first processed by Dicer into short duplexes of 21-23 nt, called short interfering RNAs (siRNAs)2. Incorporated in RNA-induced silencing complex (RISC) they are able to mediate gene silencing through cleavage of the target mRNA in the center of the region of homology by Argonaute 2, a component of RISC3. In 2001, Elbashir et al4 demonstrated that the direct introduction of synthetic siRNAs would mediate RNA interference gene silencing in drosophila but also in mammalian cells. Since then, siRNA-mediated gene silencing has become a powerful and widely-used molecular biology tool in both target identification target validation studies. Use of siRNAs for gene silencing in animal studies has been described in a limited amount of animal models. Unmodified siRNAs were delivered locally in the eye5, intrathecally or intracerebellarly in the central nervous system6, and intranasally for the inhibition of respiratory viruses7. Intravenous hydrodynamic tail vein injection of unmodified siRNAs has also been studied. This approach allows a rapid delivery, mainly to the liver8. A very limited number of studies have been reported on the systemic administration of unmodified siRNAs. Duxbury et al9 administered intravenously unmodified siRNAs targeting Focal Adhesion Kinase to an orthotopic tumor xenograft mice model, and observed a tumor growth inhibition as well as a chemosensitization to gemcitabine. Soutscheck et al reported the systemic use of highly chemically modified siRNAs for the endogeneous silencing Apolipoprotein B. Intraperitoneal administration of most anti-ApoB siRNA at the high dose of 50 mg/kg reduced ApoB protein level and Lipoprotein concentration10. Despite these examples, in vivo use of siRNAs upon systemic delivery requires improvements in order to make this technology widely applicable for target validation or therapeutic applications. Indeed, unmodified siRNAs are subject to enzymatic digestion, mainly by nucleases abundant in the blood stream. In order to improve pharmacological properties of siRNAs several groups investigated chemical modification of these reagents. While the approaches described are very different among themselves and that no systematic study was yet performed, an overview of the results allows to determine the tolerance of siRNAs to chemical modifications. Several chemistries such as phosphorothioates11 or boranophosphates12, 2′-O-Methyl13, 2′-O-allyl14, 2′-methoxyethyl (MOE) and 2′-deoxyfluoronucleotides15 or Locked Nucleic Acids (LNA)16 have been investigated. These studies highlighted that tolerance for modification is not only chemistry-dependent, but also position-dependent.
The present invention provides a minimally modified siRNA with improved pharmacological properties. The minimally modified siRNAs are 19 bp double-stranded RNA modified on the 3′-end of each strand in order to prevent 3′-exonuclease digestion: the 3′-dideoxynucleotide overhang of 21-nt siRNA has been replaced by a universal 3′-hydroxypropyl phosphodiester moiety and the modification of the two first base-pairing nucleotides on 3′-end of each strand further enhances serum stability. Applied intraperitoneally or orally to adult mice, the modified siRNAs displayed higher potency in a growth factor induce angiogenesis model which correlates with their increased serum stability.